Method of fabricating coaxial wires in back panels

ABSTRACT

The plastic insulated cross-connection wires on the backside of an electrical panel are coaxed by momentarily applying a mass of molten, low melting temperature metal to the backside of the panel with the major portion then removed. The adhering portion solidifies and the shielded cross-connections are potted in a plastic mass to maintain the wires in position and to protect the same against mechanical impact.

0 United States Patent 1151 3,659,340 Giedd et al. 1 May 2, 1972 [54]METHOD OF FABRICATING COAXIAL WIRES IN BACK PANELS [56] References Cited[72] Inventors: Gary R. Giedd; Merlyn H. Perkins, both UNITED STATESPATENTS F 11 N.Y. wappmgers a 8 3,436,604 10/1969 K1lby et al ..317/101[73] Assignee: International Business Machines Corpora- 2,960,417 11/1960 Strother .1 17/217 X tion, Armonk, NY. 2,983,031 5/1961 Blanchard..29/573 [22] Flled: 1969 Primary Examiner-John F. Campbell [21] Appl.No.: 885,639 Assistant Examiner-Robert W. Church Attorney-Sughrue,Rothwell, Mion, Zinn & Macpeak Related US. Application Data [63]Continuation-impart of Ser. No. 606,129, Dec. 30. [571 ABSTRACT 1966,abandoned The plastic insulated cross-connection wires on the backsideof an electrical panel are coaxed by momentarily applying a [52] U.S. Cl29/527.4, 29/604, 7 ma of molten low melting temperature metal to the[74/686, [74/35 R, 174/88 C, 174/102 C, 317/101 backside of the panelwith the major portion then removed. 1 14 A, 1 17/1 14 1 264/272 R Theadhering portion solidifies and the shielded cross-connec- [51] Int. Cl.B41m 3/08, l-l0lb 13/00 tions are potted i a l i mass to maintain thewires in posi- [58] FieldotSearch ..117/217,1l4A,1l4B;

tion and to protect the same against mechanical impact.

8 Claims, 3 Drawing Figures PATENTEDMY 21922 3, 659, 340

24 k 22 8' I l y '12:;

FIG. 3 2'4- I INVENTORi ,GARY R. GIEDD MERLYN H. PERKINS ATTOR NEYQCROSS REFERENCE TO RELATED APPLICATIONS Back Panel" by F. Kurtz and J.C. Logue and assigned to the common assignee.

" BACKGROUND OF THE INVENTION 1. Field of the Invention I p Thisinvention relates to a method of back panel wiring by which standard,plastic insulated, interconnecting wires may be made coax, and moreparticularly, to an improved method which insures complete coaxing ofthe back panelinterconnecting wire portions without materiallyincreasing the overall weight of the panel.

I 2. Description of Prior Art In the patent referred to above, theinterconnecting wires on the backside of a panelcarrying electroniccomponents, were appropriately shielded by applying a mass'of moltenmetal to that side of the panel and cooling the molten mass to embed thewires in solid metal. The panel itself may advantageously comprise alaminate structure including a central, imperforate, resilient sheet,sandwiched between sheets of insulative material carrying alignedthrough holes, whereby the terminal ends of the interconnecting wiresare passed through aligned holes, piercing the imperforate resilientsheet with the resilient sheet effecting a seal about the outer surfaceof the wire, while frictionally maintaining the'interconnecting wires inposition. The terminal ends of the wires,-after piercing theresilientsheet and emergence frorn'the aligned through holes, are b aredand connected to adjacent terminals carried by the panel. In the priormethod, a relatively large mass of bonding material results in a ratherheavy panel assembly which presents additional problems due to thethermal-coefficient of expansion mismatch between the metal and theepox- I SUMMARY OF THE INVENTION In general, the present invention isdirected to an improved method of electrically-shielding the syntheticresinous insulated wires carried by an electrical panel on the backsidethereof, involving the steps of momentarily applying a mass of moltenmetal having a low melting temperature to the side of the panel carryingtheinsulated wires, removing the portion of molten metal not adhering tothe insulation surrounding'the wire and solidifying'the remnant metal toefiectively'shield the wires.

- In one specific form, the method further involves the subsequent stepof potting the now coaxed wire in a plastic mass to maintain theshielded wires in position, permitting ease in handling of the panelwithout danger of mechanical impact or abrasion of the coax wireinterconnections.

The present invention provides an improved method of back panel wireshielding which insures complete shielding of the insulated wirescarried by the panel without materially increasing the overall weight ofthe panel and without introducing thermal expansion problems due to thepresence of the shielding metal. The present invention further providesan improved shielding method for back panel wiring in which theint'erconnection wiresare securely maintained in position aftershielding by means other than the metal coating the insulation of theindividual wires.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective, explodedview of a component supporting panel which is back wired and shielded bythe method of the present invention.

FIG. 2 is an elevational view, in section, of a portion of the panel ofFIG. 1, prior to back wiring and shielding; and

FIG. 3 is the same view of the panel as FIG. 2, after back wiring andshielding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, thereis shown the improved back panel of the present invention, identifiedgenerally at 10, which basically comprises first front sheet or board 12formed of plastic or'similar insulative material, a central sheet ofsilicon rubber 14 and a second insulative board or sheet 16. The frontsheet is first drilled with blind holes 20 on mil. centers, forinstance, from the outer surface 18 inwardly. Conductive metal pins 22are inserted in the blind holes and extend perpendicular to surface 18,as indicated best in FIG. 2. Four or more through holes 24 are drilledaround each pin, the holes acting as wire entrance holes. It isfurthernoted that the bottom is also provided with a like number ofthrough holes 24'. When the three sheets I2, 14 and 16 are sandwichedtogether, holes 24' match the wire entrance holes 24 carried by the rearsheet 12. The intermediate sheet of imperforate silicon rubber 14 isattached to the underside of the first plastic sheet 12 and the secondplastic sheet 16 is placed on the rubber sheet 14 to form a plasticsheet-rubber sheet-plastic sheet laminate panel structure 10. v c

The next step is the attachment of an open rectangular frame 28 to theperiphery of the laminate structureIO such that the rectangular frame 28forms a well or void area 30, on

the backside of the panel, as further defined by the bottom surface 32of the rear sheet 16. The upstanding pins 22 are provided for physicallysupporting electronic components, such as component 26 inFIG.3,.normally spaced slightly from the outer surface 18 of plastic sheet12. In addition, the pins make appropriate electrical connections tocomponent circuitry (not shown) internally of each component. I

Appropriate electrical interconnections are made between the space,insulated pins 22 in the manner shown in FIG. 3. Interconnections aremade by inserting a probe, such as a sewing needle, (not shown), fromthe backside of the panel assembly, through one of the holes 24' carriedby sheet 16 of the laminate structure. The needle pierces theimperforate rubber sheet 14 and passes next through an aligned hole 24carried by the upper panel sheet 12. For instance, end 38 of wire 36 isfed through associated aligned holes 24' and 24 by the sewing needlewith the left-hand end of the wire 38 protruding above the upper surface18 of the panel assembly. I

The panel or component receiving board of the present invention, whichpreferably comprises a laminate structure involving at least onepredrilled sheet of insulative material and an imperforate sheet ofresilient material overlying the drilled insulative sheet and coveringthe through holes, acts advantageously both to seal the non-used throughholes, as well I 'as to seal any conductor which passes through thethrough holes and pierces the imperforate, resilient layer. Further, inpiercing the resilient layer, the resilient material closely hugsthe-conductor and frictionally maintains the inserted conductor inplace, even though the conductor may be of a somewhat smaller diameterthan the through hole. Obviously, were it not for the imperforateresilient material, the conductor may have a tendency to move from itsprearranged position, prior to wire wrapping or other mode of connectionto the adjacent terminal pins 22. This is'especially so where the panelis being used as shown, with the interconnecting wires positioned on thebottom side of the panel and the components 26 on the top side.

After stripping the insulation, the bared wire end 40 is wrapped about anearby pin 22 in conventional fashion. The same procedure is repeatedwith the right-hand end 42 of wire l 36 so that the wirenowinterconnects the first and fourth pins from the left, as shown inFIG. 3. Other interconnections involving, for instance, wires 44 and4'6,'are made in a similar manner. r t

Wires 36, 44, and 46 may, for instance, comprise single or multiplestrands of copper coated by plastic insulation. Preferably, the wires.carry a Teflon coating. Teflon is a registered trademark of the DuPontCorporation, its chemical composition is polytetrafluroethylene, itsmelting temperature is 327 C, and at temperatures above 350 C., it willtend to disintegrate or decompose. Alternatively, instead of Teflon, theinterconnection wires may be coated with other suitable materialshavingelectrical insulative qualities, these materials being butyl rubber,enamel, polyethylene, silicon rubber, and n ion. -wmi theinterconnections completed, the'intermediatminsulated portions of thewire extend across the back orrear side of the panel assembly within thewell area 30 formed by the rectangular frame 28. The/next step involvesthe momentary filling of the well 30 with a. low melting temperaturemolten metal mass to effectively coat the insulated wires with a thinlayerlof metal for electrically shielding the wires. from each other.After wiring, theframe 28 may be inverted and a'low melting-temperaturemetal, in liquid form, is pured into'the well 30, filling the same.immediately, the frame 28 is turned over. that is, it is reverted to theoriginal'position shown in I F IG. 2, thereby displacing all of theliquid metal from the well with the exception of athincoat 48 whichadheres to all exposed surfaces of the insulated wires carried at thebackside of the panel. The'metal 48 may comprise a low meltingtemperature material, for instance, alloysof bismuth with metal, such astin, lead, cadmium or indium,

- .While, preferably, the low melting temperature material formingthecoaxsmetal coating 48, for. the wire interconnections 36, 44 and 40comprises alloys of bismuth, as stated above, alternative low,melting'temperature metalalloys such as indium'based alloys and typemetals may be employed. It is essential, however, that themeltingtemperature of the bath be less than. the temperature which causesinstantaneous decomposition or melting of the plastic insulationsurrounding the cross wire interconnections on the back of the panel.For

well area 30 is now in a position to receive potting material 50.

t in this case, instead of being metal, it is preferably plastic orotherlight weight insulator. The frame may be maintained in its invertedposition until complete solidification of the plastic potting materialoccurs, thereby achieving a lighter weight, back panel assembly thanthat provided by the prior art process which omits the final two steps.

' The plastic material may be similar to that of the plasti boards orsheets 12 and 16 and is both thermally and chemically compatible withthe potting metal 48 covering the wires. The potting compound 50protects the back wiring from physical damage since none of the wiringcarrying the thin metal shield remains exposed. Since only a thin layerof metal remains, the use of a plastic potting material, rather than theemployment of the metal potting technique of the above referred toapplication eliminates any thermal expansion problems which might occurif a panel carrying a large mass of metal were subjected to relativelyhigh temperature-Since all of the exposed interconnecting wires aremetal shielded, improved circuit performance is achieved. i I

Alternatively, instead of inverting the panel including the edge framemember 28 prior to momentarily allowing amass of metal to fill the wellarea, the initial thin metalcoating 48 may be applied to the insulatedwires carried in the backside of the panel by the simple step ofmomentary immersion of this portion of 'thepanel assembly 10 into amolten bath of instance, the-melting temperature'of 'l'eflon is wellabove the V I temperature of the molten bismuth alloy material which isapplied" to form the coax metal coating 48'on the interconnecvtionwires. In this case, the melting temperature of the bismuth 'alloy' isapproximately 117 C. Further, since the application of the moltenmetalmass to the insulation interconnection wires on the backside ofthe'panel 10 is only momentary, either by dipping the backside of thepanel momentarilyinto the' molte'n bath or material, or by invertingframe 28, pouring the same in liquid form into the well 30 and thenimmediately reverting the. frame 28 to its original position shown inFIG. 2, it is apparent that extended contact between the resinous coatedinterconnection wire on the backside of'the panel and the molten bathmay result in decomposition or destruction of Y the insulation on thewire even though the temperature of the metal bath or coating materialis insufficient to melt or otherwise destroy immediately the insulationof the wire upon contact therewith. Preferably, there should be atemperature gap of approximately 20 C. between the temperature of thebath and the melting or decomposition temperature of thesyntheticresinous insulation material surrounding the interconnectionwires 36, 44 and 46. Finally, it'is important that the low meltingtemperature metal 48 have some affinity to the insulatiQtt materialcoating the interconnectionwire so that under the flash coatingtechnique of the present invention there is assurance that even as aresult of the momentary contact between the interconnection wires on thebackside of the panel and the mass of molten low melting temperaturemetal 48, a thin coating of the same readily applies and is evenlydistributedover the same.

' 'After the displacement of the major'mass of the low temmetal (notshown). Upon removal, some metal will adhere to the surface oftheinsulated wire such that upon cooling, the insulated interconnectionwire coaxed as described. 7

in fact, the plastic material 50 which embeds the now coaxed wire, maybe applied by dipping of the metal coated, back wired panel into asecond bath, of molten plastic and cooling the molten plastic wirevwith-the panel wire so im mersed'to produce a complete panel section,'asindicated in FIG. 3.

While it is normally undesirable to make any wiring changes subsequentto plastic potting-wiring changes may be achieved upon removal of theplastic'potting material 50. The application of high temperature meltsthethin layer'of shielding material 48 about the interconnectingportions of the wires, whereuponany wires which must be removed, may bereadily pulled from the aligned through holes 24 and '24 afterdisconnecting the bared terminal ends from associated terminal pins.

Further, in case thel remo ve'd wires are not replaced, the wireentrance holes that had wires taken out will automatically be sealed bytheresilient rubber sheet which retracts about the area of penetrationand seals the vacant holes. After rewiring, the well 30 may againmomentarily refilled with liquid metal to achieve shielding of thereplaced insulated wires, after which the same area may be subsequentlyfilledwith plastic material to mechanically protect the shieldedinterconnecting wires.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that the foregoing and other changes in the form anddetails may be made therein without departing from the spirit and scopeof the invention.

We claim: v

1. A method of electrically shielding insulated wires insulated by asynthetic resinous material and carried on one side of an electricalpanel provided on an opposite side thereof with component mounting meanshaving terminals for electrical connection to electronic components,comprising the steps of:

A. mounting a said wire through said panel with an end portion thereofextending above said opposite side;

B. securing said end portion in electrically conducting relation to asaid terminal of said mounting means;

C. momentarily applying a mass of molten metal having a low temperaturemelting point to the said one side of said panel carrying said insulatedwires and in contact therewith; and

perature metal, the frame 28 may again be inverted so that the D.coating the wire insulation with a thin metal film by portions are metalcoated or a. removing the major mass of said molten metal prior to anymelting of the wire insulation, and

b. cooling the remnant metal on the wire insulation to effect coating ofthe wire insulation with said thin metal film.

2. The method as claimed in claim 1 wherein the temperature gap betweenthe temperature of the applied molten metal and the melting temperatureof the synthetic resinous wire insulation-is approximately 3. The methodas claimed in claim 1 wherein said low temperature melting point metalcomprises alloys of bismuth with one metal of the group consisting oftin, lead, cadmium or indium, and said wires are coated bypolytetraflorethylene insulation material.

4. The method as claimed in claim 1 further including the step ofpotting the metal coated wires with a mass of plastic material to embedthe metal coated wires in a solid plastic mass to increase panelrigidity while physically protecting the interconnecting wires.

5. The method as claimed in claim 1 wherein the step of momentarilyapplying a mass of molten metal to the side of the panel carrying saidinsulated wires comprises momentary dipping of said wired back panelinto a bath of molten metal and immediately removing the same whereby athin layer of molten material adheres to the insulation covering saidwires.

6. The method as claimed in claim 1 for a back panel including a framemember extending about the periphery of said panel backside and actingin conjunction therewith to form a well area, said method furtherincluding the steps of; positioning said panel with the well side up,filling said well area with liquid plastic material and cooling saidassembly to embed the coated insulated wire portions in a solid plasticmass to produce a high strength, light weight panel having metalshielded wire interconnections.

7. The method as claimed in claim 1 wherein said low melting temperaturemolten metal mass comprises one material of the group consisting of;alloys of bismuth with tin, lead, cadmium or indium, and antimony, andsaid wire is coated with one insulation material of the group consistingof polytetraflorethylene, butyl rubber, enamel, polyethylene, nylon andsilicon rubber.

8. The method of claim 1 wherein said wire is mounted in sealingconformation through said panel.

2. The method as claimed in claim 1 wherein the temperature gap betweenthe temperature of the applied molten metal and the melting temperatureof the synthetic resinous wire insulation is approximately 20*.
 3. Themethod as claimed in claim 1 wherein said low temperature melting pointmetal comprises alloys of bismuth with one metal of the group consistingof tin, lead, cadmium or indium, and said wires are coated bypolytetraflorethylene insulation material.
 4. The method as claimed inclaim 1 further including the step of potting the metal coated wireswith a mass of plastic material to embed the metal coated wires in asolid plastic mass to increase panel rigidity while physicallyprotecting the interconnecting wires.
 5. The method as claimed in claim1 wherein the step of momentarily applying a mass of molten metal to theside of the panel carrying said insulated wires comprises momentarydipping of said wired back panel into a bath of molten metal andimmediately removing the same whereby a thin layer of molten materialadheres to the insulation covering said wires.
 6. The method as claimedin claim 1 for a back panel including a frame member extending about theperiphery of said panel backside and acting in conjunction therewith toform a well area, said method further including the steps of;positioning said panel with the well side up, filling said well areawith liquid plastic material and cooling said assembly to embed thecoated insulated wire portions in a solid plastic mass to produce a highstrength, light weight panel having metal shielded wireinterconnections.
 7. The method as claimed in claim 1 wherein said lowmelting temperature molten metal mass comprises one material of thegroup consisting of; alloys of bismuth with tin, lead, cadmium orindium, and antimony, and said wire is coated with one insulationmaterial of the group consisting of polytetraflorethylene, butyl rubber,enamel, polyethylene, nylon and silicon rubber.
 8. The method of claim 1wherein said wire is mounted in sealing conformation through said panel.